Biological vessels of humans and animals carry fluids necessary to sustain life. Obstructions to the flow of fluids through these vessels can occur due to an accumulation of material caused by disease or other conditions. For example, plaque can form in cardiovascular systems because of heart disease, poor diet or heredity. Over time, the plaque can build up within the vessels supplying blood to the heart, for example, and block the flow of blood to the organ causing heart attacks or the like. The buildup of obstructive deposits in other vessels of the subject organism as well can lead to damage or failure of the corresponding organ dependent upon the biological fluid communicated by the vessel.
Plaque can be mechanically removed from vascular systems through various surgical procedures. However, this option is undesirable because it is expensive, highly invasive, and requires a long recovery time.
Angioplasty provides a non-surgical solution to the buildup of plaque in vascular systems. In this procedure, a catheter is introduced into the vascular system, usually through an artery such as the femoral artery. A small specialized deflated balloon is carried on the distal end of the catheter so that it may be positioned adjacent to the blockage area in accordance with corresponding guided movement of the catheter body. Once positioned, the balloon is temporally inflated causing the balloon to expand and the plaque accumulation to be compressed radially outwardly against the inner wall of the lumen of the target vessel. Thereafter, the catheter and balloon may be removed leaving an impression of the inflated balloon on the compressed plaque in the form of a smooth widened passage of the lumen of the vessel.
Proper routing of the balloon prior to inflation is important during angioplasty. For this, some catheters carry small cameras or other local visualization equipment to provide visual feedback to the interventionist of the position of the balloon relative to the target site. Post procedure visualization of the treatment area is not possible, however, because the cameras are removed from the patient together with retraction of the host catheter after the procedure.
Other methods used to insure positioning of the balloon relative to the plaque buildup during the procedure include concurrent imaging of the site using ultrasonic, CT, and/or MRI scanning technologies. However, MRI scanning is expensive and time consuming, and many patients prefer to avoid exposure to X-rays from CT procedures.
In some cases, mechanical devices such as stents have been placed at the target site directly after or during angioplasty for purposes of helping to prop open the target vessel. Typical stents are formed as a small expandable tube of shape retaining plastic material or an expandable shape retaining metal mesh. The stent is carried on the balloon area of the catheter and is thereby introduced into the target site during the angioplasty procedure at an operative position between the balloon and the inner wall of the lumen of the target vessel. Inflation of the balloon causes a coincident expansion of the stent. In the expanded conformation, the shape retaining stent is functional to hold the vessel open thereby enhancing the ability of the vessel to pass fluids therethrough well after the balloon is deflated and after the catheter is decoupled from the stent and withdrawn from the patient.
In addition to the post-procedure mechanical benefits afforded by stent devices, typical drug-eluting stents carry one or more medicaments for diffusion thereof over one or more predetermined time periods. One such medicament is aspirin and clopidogrel for reducing the risk of thrombosis leading to stent occlusion during the procedure or in the days following, or later.
Despite advances made in angioplasty procedures and in stent development, however, certain issues remain. Many patients experience a re-accumulation of plaque buildup. In some cases about 37% of the plaque returns in the patients' veins in the first 12 months after the procedure. A 10% buildup of plaque after the first month is not uncommon in some patients.
Unfortunately, inexpensive and non-invasive detection of post-procedure plaque re-accumulation is not available. Follow up CT scans expose the patients to undesirable X-rays and MRI sessions are time consuming and expensive. Post-angioplasty catheterization procedures are likewise time consuming but also introduce invasive equipment into the patients' body and, accordingly, carry some risks.
Methods and apparatus providing in situ detection, visualization, and assessment of the buildup of material such as plaque in vascular systems of humans and animals are therefore desirable.